Multi-band built-in antenna for independently adjusting resonant frequencies and method for adjusting resonant frequencies

ABSTRACT

The invention relates to built-in antenna. Specifically, a multi-band built-in antenna having plurality of resonant frequencies and a method for adjusting resonant frequencies are provided, wherein resonant frequencies are able to be adjusted independently without affecting one another, for each resonant frequencies are adjusted separately through separate radiating elements.

TECHNICAL FIELD

The invention relates to built-in antenna. Specifically, a multi-bandbuilt-in antenna having plurality of resonant frequencies and a methodfor adjusting resonant frequencies are provided, wherein resonantfrequencies are able to be adjusted independently without affecting oneanother, for each resonant frequencies are adjusted separately throughseparate radiating elements.

BACKGROUND ART

Antennas are conductors placed in space to radiate radio waves or induceelectromagnetic force effectively in the space for communication, ordevices for receiving and transmitting electromagnetic waves.

Antennas have common basic principles, but the shapes of antennas varywith the frequency used, to which the antennas are made to resonate foreffective operation.

However, for there are various radio communication standards, which usedifferent frequencies to one another, an antenna must have a pluralityof resonant frequencies to be used for all standard. Further, recentlyportable radio communication devices have integrated functions includingGPS, data communication, authentication, e-payment, etc. as well asvoice communication, expanding application thereof, and these functionsuse different frequency bands, increasing the need for multi-bandantenna.

For example, there exists the need for operating one radio communicationdevice at 800 MHz band for DCN (Digital Cellular Network), GSM850 andGSM900, 1800 MHz band for K-PCS, DCS-1800 and USPCS, 2 GHz for UMTS, 2.4GHz for WLL, WLAN and Bluetooth, and 2.6 GHz for satellite DMB, growingnecessity of developing multi-band antennas.

In the meantime, radio communication device, which has become anecessity in modern life, tends to be smaller and lighter and so doesantenna. Therefore, in these days antenna developers are in a technicaland strategic position where they have to develop smaller buthigh-performance antennas.

Especially, recently the design of mobile radio communication devicebecome various and built-in antennas that allow for high degree offreedom without affecting appearance of the device are employed muchmore than the past. In accordance, the main task in antenna research anddevelopment is to implement multi-band antenna having a plurality ofresonant frequencies in limited and narrow interior space ofcommunication devices effectively.

For convenience, conventional multi-band antennas are shown in FIGS. 1,3 and 5.

FIG. 1 shows a conventional triple-band antenna. The antenna comprisesground plane 60, feed part 40, ground part 50, and the first to thirdradiating elements 10, 20 and 30. The conventional antenna exhibitstriple band resonance characteristic, as shown in FIG. 2. In otherwords, the antenna of FIG. 1 has three resonant frequencies includingthe first resonant frequency around 800 MHz, the second resonantfrequency around 1.8 GHz, and the third resonant frequency around 2.4GHz. These resonant frequencies are determined by electrical lengths ofthe first radiating element 10, the second radiating element 20 and thethird radiating element 30, respectively.

As shown in FIG. 3, if the second radiating element 20 is removed fromthe triple-band antenna of FIG. 1, it exhibits a resonant characteristictotally different from what it showed before with the third resonantfrequency moved toward 1.8 GHz band as shown in FIG. 4.

Similarly, if the third radiating element 30 is removed from theconventional triple-band antenna as shown in FIG. 5, the first resonantfrequency moves toward high frequency region, thus the frequencycharacteristics around the second resonant frequency is also changeddrastically.

Generally, because for multi-band antennas, radiating elements should beplaced in narrow and limited space achieving multi-resonantcharacteristics, radiating elements with various lengths, widths, andshapes are employed. In this case, as above, when adjusting one ofresonant frequencies, another resonant frequency is changed due to theundesired inter-element effect.

Therefore, to set desired multi-band resonant frequencies, one resonantfrequency is adjusted first, another frequency is adjusted, and finally,the resonant frequency adjusted previously has to be re-adjusted finely.Accordingly, as the number of radiating elements, thus number offrequency bands increases, the number of steps needed to adjust resonantfrequencies increases exponentially and too much time and effort arerequired to develop an antenna.

DISCLOSURE OF INVENTION

Technical Problem

It is an object of the invention to provide a multi-band antenna andmethod for adjusting resonant frequencies for adjusting resonantfrequencies of the antenna accurately by adjusting only a part ofradiating elements of the antenna.

It is also an objective of the invention to provide a multi-band antennaand method for adjusting resonant frequencies for adjusting resonantfrequencies independently to one another without redundant adjustment.

Technical Solution

According to one aspect of the invention, present invention provides amulti-band built-in antenna, comprising: a main radiating elementconnected to a ground part and a feed part, the main radiating elementbeing parallel to a ground plane; a secondary radiating element arrangedparallel to the main radiating element; and a connecting elementconnecting the main radiating element and the secondary radiatingelement, which defines a slit between the main radiating element and thesecondary radiating element, wherein the secondary radiating element hasa length such that the antenna resonates to a first resonant frequency,and the connecting element has a width such that the antenna resonate toa second resonant frequency.

It is preferred that the first resonant frequency is in the frequencyband used for DCN (Digital Cellular Network), and the second resonantfrequency is in the frequency band used for DMB (Digital MultimediaBroadcasting).

According to another aspect, present invention provides the multi-bandbuilt-in antenna according to claim 1, further comprising an additiveradiating element connected to and arranged coplanar with the mainradiating element, wherein the additive radiating element has anelectrical length such that the antenna resonates to a third resonantfrequency.

It is preferred that the additive radiating element is of a meandershape, and an end portion of the meander shape has a width such that theantenna resonates to the third resonant frequency.

Further, preferably, the additive radiating element is arranged insidethe main radiating element.

In addition, it is preferred that, the first resonant frequency is inthe frequency band used for DCN (Digital Cellular Network), the secondresonant frequency is in the frequency band used for DMB (DigitalMultimedia Broadcasting), and the third resonant frequency is in thefrequency band used for K-PCS (Korea-Personal Communications Services).

The antenna may further comprise a dielectric body supporting the mainradiating element, the secondary radiating element and the connectingelement.

According to further aspect of the invention, present invention providesa method for adjusting resonant frequencies of a multi-band built-inantenna comprising a main radiating element connected to a ground partand a feed part, the main radiating element being parallel to a groundplane, a secondary radiating element arranged parallel to the mainradiating element, and a connecting element connecting the mainradiating element and the secondary radiating element, which defines aslit between the main radiating element and the secondary radiatingelement, comprising:

adjusting a first resonant frequency roughly by setting total length ofthe main radiating element, the secondary radiating element, and theconnecting element to λ₁/4, wherein λ₁ is a wavelength corresponding toa first target resonant frequency;

adjusting a second resonant frequency roughly by setting a length of theslit to λ₂/4, wherein λ₂ is a wavelength corresponding to a secondtarget resonant frequency;

adjusting the first resonant frequency finely by adjusting a length ofthe secondary radiating element; and

adjusting the second resonant frequency finely by adjusting a width ofthe connecting element.

Here, the adjusting the first resonant frequency roughly and theadjusting the second resonant frequency roughly may be performedconcurrently.

It is preferred that the first resonant frequency is in the frequencyband used for DCN (Digital Cellular Network), and the second resonantfrequency is in the frequency band used for DMB (Digital MultimediaBroadcasting).

According to another aspect, present invention provides, a method foradjusting resonant frequencies of a multi-band built-in antennacomprising a main radiating element connected to a ground part and afeed part, the main radiating element being parallel to a ground plane,a secondary radiating element arranged parallel to the main radiatingelement, a connecting element connecting the main radiating element andthe secondary radiating element, which defines a slit between the mainradiating element and the secondary radiating element, and an additiveradiating element connected to and arranged coplanar with the mainradiating element, comprising:

adjusting a first resonant frequency roughly by setting total length ofthe main radiating element, the secondary radiating element, and theconnecting element to λ₁/4, wherein λ₁ is a wavelength corresponding toa first target resonant frequency;

adjusting a second resonant frequency roughly by setting a length of theslit to λ₂/4, wherein λ₂ is a wavelength corresponding to a secondtarget resonant frequency;

adjusting a third resonant frequency by setting an electrical length ofthe additive radiating element to λ₃/4, wherein λ₃ is a wavelengthcorresponding to a third target resonant frequency;

adjusting the first resonant frequency finely by adjusting a length ofthe secondary radiating element; and

adjusting the second resonant frequency finely by adjusting a width ofthe connecting element.

The adjusting the first resonant frequency roughly and the adjusting thesecond resonant frequency roughly may be performed concurrently.

Further, the additive radiating element may be of a meander shape, andthe adjusting the third resonant frequency may comprise adjusting thethird resonant frequency finely by adjusting a width of an end portionof the meander shape.

Preferably, the first resonant frequency is in the frequency band usedfor DCN (Digital Cellular Network), the second resonant frequency is inthe frequency band used for DMB (Digital Multimedia Broadcasting), andthe third resonant frequency is in the frequency band used for K-PCS(Korea-Personal Communications Services).

Advantageous Effects

According to the invention, it is possible to adjust resonantfrequencies of an antenna by adjusting dimension of only a part of theantenna, and to adjust plurality of resonant frequencies each of whichis adjusted independently avoiding repetitive adjustments.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and nature of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify correspondingly throughout and wherein:

FIG. 1 shows a conventional triple-band built-in antenna;

FIG. 2 shows resonant characteristics of the conventional triple-bandantenna;

FIG. 3 shows the built-in antenna in which the second radiating elementis removed from the triple-band built-in antenna of FIG. 1;

FIG. 4 shows the resonant characteristics of the built-in antenna ofFIG. 3;

FIG. 5 shows the built-in antenna in which the third radiating elementis removed from the triple-band built-in antenna of FIG. 1;

FIG. 6 shows the resonant characteristics of the built-in antenna ofFIG. 5;

FIG. 7 shows a dual-band built-in antenna according to an embodiment ofthe invention;

FIG. 8 shows the change in resonant characteristics of the built-inantenna of FIG. 7 according to the change of the width of the connectingelement;

FIG. 9 shows a triple-band built-in antenna in which the additiveradiating element is added to the antenna of FIG. 7;

FIG. 10 shows the change in resonant characteristics of the antenna dueto adding the additive radiating element;

FIG. 11 shows the resonant characteristics of the triple-band built-inantenna of FIG. 10 according to the change of the width of the endportion of the additive radiating element;

FIG. 12 is a flowchart illustrating the method for adjusting resonantfrequencies of a dual-band antenna according to an embodiment of theinvention; and

FIG. 13 is a flowchart illustrating the method for adjusting resonantfrequencies of a triple-band antenna according to another embodiment ofthe invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Below, referring to accompanying drawings, the preferred embodiment ofthe invention is described in detail. It is omitted the description ofthe well-know functions and components which could blur the essence ofthe invention.

FIG. 7 shows a dual-band built-in antenna according to an embodiment ofthe invention. The dual-band built-in antenna may comprise, as shown inFIG. 7, a main radiating element 100, connecting element 130 andsecondary radiating element 120, the main radiating element 100 beingconnected to an feed part 140 and ground part 150.

The main radiating element 100, the connecting element 130 and thesecondary radiating element 120 may constitute a radiator as a whole,determining the first resonant frequency. That is, when the wave lengthcorresponding to the first target resonant frequency is λ₁, the totallength (L1+L2+L3) of the main radiating element 100, connecting element130, and the secondary radiating element 120 may be determined as λ₁/4,determining the first resonant frequency. Further, in determining thefirst resonant frequency, it is possible to adjust the first resonantfrequency of the antenna finely by adjusting only the length L3 of thesecondary radiating element 120, which is a part of the radiator.

The main radiating element 100 and the secondary radiating element 120arranged parallel thereto may define a gap between them, determining thesecond resonant frequency. Specifically, the gap between the mainradiating element 100 and the secondary radiating element 120 mayfunction as a slit of radiator, having the antenna resonate at thesecond resonant frequency. Here, the length of the slit, which is thelength (L3-W1) from the end of connecting element 130 to the end of thesecondary radiating element 120, may be set to λ₂/4, wherein λ₂ is thewave length corresponding to the second target resonant frequency.Therefore, by adjusting the width W1 of the connecting element 130, thelength of slit may be adjusted and eventually the second resonantfrequency adjusted.

Upon adjusting the width W1 of the connecting element 130, the firstresonant frequency determined by the length L1+L2+L3 does not alter.Therefore, according to the present embodiment, after setting the firstresonant frequency, the second resonant frequency may be adjusted to thetarget frequency independently and two resonant frequencies can beadjusted simply and quickly without repetitive adjustments.

While only elements 100, 120, 130 of the antenna are shown in FIG. 7, itis possible to place a dielectric body, preferably box-shaped, inconjunction with the elements 100, 120, 130 to support them and improvethe characteristics of the antenna.

As an implementation of the dual-band antenna according to theinvention, there were presented the main radiating element 100, theconnecting element 130 and the secondary radiating element 120 in thespace of 30 mm width, 8 mm length, and 5 mm height (from the groundplane). The lengths (L1, L2, L3) of main radiating element 100, theconnecting element 130, and the secondary radiating element 120 were setsuch that the first resonant frequency was in 800 MHz band used for DCN,and the length (L3-W1) of the slit between the main radiating element100 and the secondary radiating element 120 was set such that the secondresonant frequency was in 2.6 GHz band used for DMB. Then the secondresonant frequency was adjusted finely by adjusting the width W1 of theconnecting element 130, and the resultant resonant characteristics aredepicted in FIG. 8. It was assured that the change in the width W1 alteronly the second resonant frequency not changing the first resonantfrequency as shown in FIG. 8.

FIG. 9 shows a triple-band built-in antenna according to anotherembodiment of the invention, where the lengths L1, L2, L3 are notindicated for clarity, which are the same as in FIG. 7. The triple-bandbuilt-in antenna according to the invention may further comprise anadditive radiating element 110 added to the antenna of previousembodiment.

The main radiating element 100, the connecting element 130 and thesecondary radiating element 120 may constitute a radiator as a whole,the total length (L1+L2+L3) of which may be set to λ₁/4, determining thefirst resonant frequency, wherein λ₁ is the wave length corresponding tothe first target resonant frequency. In determining the first resonantfrequency, it is possible to adjust the first resonant frequencyaccurately by adjusting only the length L3 of the secondary radiatingelement 120 finely, which is a part of the radiator.

The main radiating element 100 and the secondary radiating element 120arranged parallel thereto may define a slit with length of λ₂/4,determining the second resonant frequency, wherein λ₂ is the wave lengthcorresponding to the second target resonant frequency. Therefore, byadjusting the width W1 of the connecting element 130, it is possible toadjust the length of the slit L3-W1, thus the second resonant frequency.

The additive radiating element 110 arranged coplanar with the mainradiating element 100 may determine the third resonant frequency. Thatis, the additive radiating element 110 may have the electrical length ofλ₃/4 and resonate at the third resonant frequency, wherein λ₃ is thewave length corresponding to the third resonant frequency. The additiveradiating element may arranged inside the main radiating element 100 inmeander shape, minimizing the space antenna occupies. While the firstand second resonant frequency may be altered slightly upon addition ofadditive radiating element 110, the change can be compensated by fineadjustments of the length L3 of the secondary radiating element and thewidth W1 of the connecting element, which may be performed independentlyto each other.

Meanwhile, the third resonant frequency may be adjusted accurately byadjusting the width W2 of the end portion of the additive radiatingelement 110 of meander shape. The third resonant frequency may beadjusted because the change in width W2 alters the electrical length ofthe additive radiating element 110. For the change in the width W2,however, does not affect the lengths L1, L2, L3 and the width W1, thethird resonant frequency may be adjusted independently to the first andthe second resonant frequency without altering them.

FIG. 10 depicts the change in radiating characteristics of theimplemented antenna due to the addition of the additive radiatingelement 110 to the implementation of previous embodiment. The length ofthe additive radiating element 110 was set such that it resonated in thefrequency band used for K-PCS. As shown in FIG. 10, the third resonantfrequency was introduced in 1.8 GHz band used for PCS and the first andsecond frequencies altered due to addition of the additive radiatingelement 110. The change in the frequencies, however, were small as about40 MHz, it was assured that they could be adjusted by adjusting thelength L3 of the secondary radiating element 120 and the width W1 of theconnecting element 130.

FIG. 11 shows resonant characteristics of the implemented antennaaccording to the change of width W2. As shown in FIG. 11, it was assuredthat the change in the width W2 results in the change in the thirdresonant frequency in 1.8 GHz band, but the first and second resonantfrequencies are barely affected. Therefore, it was possible to adjustthe third resonant frequency without affecting the first and the secondresonant frequencies after setting them, and to implement a triple-bandantenna without repetitive fine adjustment of resonant frequencies.

While only elements 100, 110, 120, 130 of the antenna are shown in FIG.9, it is possible to place a dielectric body, preferably box-shaped, inconjunction with the elements 100, 110, 120, 130, to support them andimprove the characteristics of the antenna.

The method for adjusting resonant frequencies of multi-band built-inantenna according to the invention is described below.

According to an embodiment of the invention, provided is the method foradjusting the resonant frequencies of a dual-band antenna. In thisembodiment, referring to FIG. 7 and 12, initially the total lengthL1+L2+L3 of the main radiating element 100, the connecting element 130and the secondary radiating element 120 is set to adjust the firstresonant frequency roughly in step S100. In this step S100, the totallength L1+L2+L3 of the main radiating element 100, the connectingelement 130 and the secondary radiating element 120 may be set to λ₁/4,wherein λ₁ is the wave length corresponding to the first target resonantfrequency.

Then, the second resonant frequency is adjusted roughly in step S110, bysetting the length L3-W1 of the slit defined by the main radiatingelement 100 and the secondary radiating element 120 to λ₂/4, wherein λ₂is the wave length corresponding to the second target resonantfrequency.

Although the steps S100 and S110 are described as separate steps, it ispossible to perform them concurrently upon preparation of the elements100, 120, and 130. Therefore, the rough adjustment of the first andsecond frequencies may be achieved at the same time in producing theradiator including elements 100, 120, and 130.

Because antenna of the invention is not a simple monopole antenna, buthas a gap between the main radiating element 100 and the secondaryradiating element 120, resonant may not occur at the first targetresonant frequency when the total length L1+L2+L3 is exactly λ₁/4. Thus,in step S120, the length L3 of secondary radiating element 120 may beadjusted, the first resonant frequency be adjusted finely and the exactresonant frequency which is the same as the first target resonantfrequency be achieved.

Then, the length L3-W1 of the slit is adjusted finely by adjusting thewidth W1 of the connecting element 130, and the second resonantfrequency is adjusted accurately to the second target resonant frequencywithout change in the first resonant frequency in step S130. The tworesonant frequencies can be adjusted quickly and accurately, because thefirst resonant frequency is not altered by change in the width W1 of theconnecting element 130.

According to the embodiment, resonant frequencies of the antenna can beadjusted by adjusting the dimension of parts of radiator such as thesecondary radiating element 120 and the connecting element 130, not ofthe whole radiator. Further, because each dimensions only affectscorresponding resonant frequencies, it is possible to adjust tworesonant frequencies simply and accurately without repetitiveadjustments.

According to another embodiment of the invention, there is provided amethod for adjusting resonant frequencies of a triple-band built-inantenna.

Referring to FIGS. 9 and 13, initially the first resonant frequency isadjusted roughly by setting the total length (L1+L2+L3) of the mainradiating element 100, the connecting element 130, and the secondaryradiating element 120 to λ₁/4 in step S200, wherein λ₁ is the wavelength corresponding to the first target resonant frequency. Further, instep S210, setting the length L3-W1 of the slit defined by the mainradiating element 100 and the secondary radiating element 120 to λ₂/4,the second resonant frequency is adjusted roughly, wherein λ₂ is thewave length corresponding to the second target resonant frequency.

Then, the third resonant frequency is adjusted roughly by setting thelength of additive radiating element 110 to λ₃/4 in the step S220,wherein λ₃ is the wave length corresponding to the third resonantfrequency. As described above, in this step, the first and secondresonant frequencies may be changed slightly due to the addition of theadditive radiating element 110.

Although the steps S200 and S210 are described as separate steps, it ispossible to perform them concurrently upon preparation of the elements100, 120, and 130. Further, it is possible to perform the steps S200,S210 and S220 concurrently upon preparation of the elements 100, 110,120, and 130. In this case, the rough adjustment of the first to thirdresonant frequencies may be achieved at the same time in producing theradiator including elements 100, 110, 120, and 130.

As mentioned above, due to the gap between the main radiating element100 and the secondary radiating element 120, and the addition of theadditive radiating element 120, the first resonant frequency may bedifferent from the first target resonant frequency. Thus, in step S230,the first resonant frequency may be adjusted finely. The first resonantfrequency may be adjusted to the first target resonant frequencyaccurately by adjusting the length L3 of the secondary radiating element120.

Next, the second resonant frequency is adjusted finely in step S240. Thesecond resonant frequency may be adjusted to the second target resonantfrequency accurately by adjusting the width W1 of the connectingelement, thus the length of the slit L3-W1 between the main radiatingelement 100 and the secondary radiating element 120. Varying the widthW1 does not affect the first resonant frequency and the second resonantfrequency can be adjusted simply and independently.

Finally, by adjusting the length of the additive radiating element 110,the third resonant frequency is adjusted to the third target resonantfrequency in step S250. It is preferred that the additive radiatingelement 110 has a shape of meander for antenna to have the thirdresonant frequency in spite of the limited space inside a mobile phone,and the fine adjustment of the third resonant frequency may be performedthrough adjustment of the width W2 of a end portion of the additiveradiating element 110. As mentioned above, varying the width W2 does notaffect the first and second resonant frequency, and the third resonantfrequency can be adjusted independently.

According to the present embodiment, resonant frequencies of an antennacan be adjusted by adjusting dimensions of only parts of the radiatorsuch as the secondary radiating element 120, the connecting element 130and the additive radiating element 110. In addition, because each of thedimensions affects only the corresponding resonant frequency, threeresonant frequencies can be adjusted simply and accurately withoutrepetitive adjustments.

The multi-band built-in antenna according to the invention can beapplied the space of 30˜40 mm width and 60˜100 mm length, and it ispossible to apply it to the mobile phones of folder-type and slide-typeas well as of bar-type.

Although the invention has been described with reference to specificembodiments, various modifications to these embodiments will be readilyapparent to those skilled in the art without departing from the spiritor scope of the invention. For example, a quad- or more-band antenna canbe produced by adding another radiating element to the embodiment of theinvention. Further, the method for adjusting resonant frequency of theinvention may be applied to quad- or more-band antennas as well as dual-or triple-band one. Also, the order of the steps described in aboveembodiments are not absolute, and various modifications to the orderwill be readily apparent to those skilled in the art without departingfrom the spirit or scope of the invention.

Thus, the present invention is not intended to be limited to theembodiments shown herein but is to be accorded the widest scope definedby appended claims and the equivalents thereto.

1. A multi-band built-in antenna, comprising: a main radiating elementconnected to a ground part and a feed part, the main radiating elementbeing parallel to a ground plane; a secondary radiating element arrangedparallel to the main radiating element; and a connecting elementconnecting the main radiating element and the secondary radiatingelement, which defines a slit between the main radiating element and thesecondary radiating element, wherein the secondary radiating element hasa length such that the antenna resonates to a first resonant frequency,and the connecting element has a width such that the antenna resonate toa second resonant frequency.
 2. The multi-band built-in antennaaccording to claim 1, wherein the first resonant frequency is in thefrequency band used for DCN (Digital Cellular Network), and the secondresonant frequency is in the frequency band used for DMB (DigitalMultimedia Broadcasting).
 3. The multi-band built-in antenna accordingto claim 1, further comprising an additive radiating element connectedto and arranged coplanar with the main radiating element, wherein theadditive radiating element has an electrical length such that theantenna resonates to a third resonant frequency.
 4. The multi-bandbuilt-in antenna according to claim 3, wherein the additive radiatingelement is of a meander shape, and an end portion of the meander shapehas a width such that the antenna resonates to the third resonantfrequency.
 5. The multi-band built-in antenna according to claim 3 orclaim 4, wherein the additive radiating element is arranged inside themain radiating element.
 6. The multi-band built-in antenna according toclaim 3 or claim 4, wherein the first resonant frequency is in thefrequency band used for DCN (Digital Cellular Network), the secondresonant frequency is in the frequency band used for DMB (DigitalMultimedia Broadcasting), and the third resonant frequency is in thefrequency band used for K-PCS (Korea-Personal Communications Services).7. The multi-band built-in antenna according to any one of claims 1 to4, further comprising a dielectric body supporting the main radiatingelement, the secondary radiating element and the connecting element. 8.The multi-band built-in antenna according to claim 1, wherein the firstresonant frequency is adjusted by setting the total length of the mainradiating element, the secondary radiating element, and the connectingelement to λ₁/4, wherein λ₁ is a wavelength corresponding to a firsttarget resonant frequency.
 9. The multi-band built-in antenna accordingto claim 1, wherein the second resonant frequency is adjusted by settinga length of the slit to λ₂/4, wherein λ₂ is a wavelength correspondingto a second target resonant frequency.
 10. The multi-band built-inantenna according to claim 1, wherein the first resonant frequency isfinely adjusted by adjusting a length L3 of the secondary radiatingelement and the second resonant frequency is finely adjusted byadjusting a width W1 of the connecting element.
 11. The multi-bandbuilt-in antenna according to claim 1, wherein the third resonantfrequency is adjusted by setting an electrical length of the additiveradiating element to λ₃/4, wherein λ₃ is a wavelength corresponding to athird target resonant frequency.